In case you didn't know the only difference between the platinum pro and the regular audigy 2 ZS is the external box. If you have no need for an external box with extra connectors then I would just get the regular audigy 2 ZS.

The card itself goes into a PCI slot. With the audigy 2 ZS pro there is an extra box with extra connectors in it that goes into the 5.25 inch bay. This is only necessary if you really want these extra connectors though, if you only have one set of speakers or the headset you only need the card, and you can connect through the back. The Audigy 2 ZS platinum Pro has the extra box with extra connectors as external instead of fitting in a 5.25 inch bay. Both the boxes are about the same with volume knobs and what not, and both come with a remote. The only real difference is one is internal the other is external.
Hope you can understand my explanation.

oh, so if i am running out of 5.25 inch bays, i go for the platinum pro

what kind of remote do they come with?IR?
i suppose there is some sort of cable connecting the 5.25 inch box to the PCI card in the case of the 2 ZS pro and in the case of the 2 ZS platinum pro there is some sot of cable which comes out of the back of the computer case to connect to the external box, correct?

Yes that's all correct. I'm not sure about the remote though, but I assume it is infrared.

Also have you considered the audigy 4 pro? It comes with an external box like the audigy 2 zs platinum pro but it is a better sound card. If you can afford it I would get that since it's the latest sound card and not too much more expensive over the audigy 2 zs platinum pro. Should be only about 20 pounds more (if I did that conversion right).